Moss growing on trees, walls, and concrete?!

I had never seen moss growing on trees, walls or concrete where I grew up in San Bernardino County. It's one of the biggest counties in the US (maybe the biggest), but most of it is desert. The cities of San Bernardino and Rialto (where I grew up), both in SB County, are classified as semi-arid, as the average rainfall there is 16.43 inches of rain per year. Areas which receive 10 to 20 inches of rain are considered semi-arid.
This is what most of San Bernardino looks like in the valley away from urban areas and also in the high desert north of the San Bernardino Mountains.

In the 1950s when I lived in the city of San Bernardino, I'd see tumbleweeds rolling across the street as I walked to school, pushed along by the hot dry Santa Ana winds in the fall. That was the inspiration for "Santa Ana Conditions," my 55 Flash Fiction story:

High warm winds blew grit into Jana’s legs like ants biting her as she walked to school. Tumbleweeds rolled across the dry field, bounced into the road and stopped at a fence ahead of her. It was 1956 and the Santa Ana winds were ripping through San Bernardino. It was a metaphor for her life.

Even in the urban areas sometimes you see tumbleweeds being blown across a road from an empty field where they had grown...

...often getting hung up on a curb, hedge or fence. They are not pretty.

Now I'm not saying that there was no moss growing on trees in San Bernardino, just not in the valley where I lived. For three summers I went to Girl Scout Camp up in the mountains near Mount San Gorgonio and on hikes in the woods we would occasionally see a little bit of moss growing on a tree near a seasonal creek. I was fascinated to see it and thrilled to be in a forest near a stream. It was so different from the desert-y place where I lived. Girl Scout Camp (Camp Tautona) is where I learned that moss grows on the north side of a tree, so if I ever got lost in a forest, at least I'd know which way was north.

Now I live in El Dorado County, northern California, in the mountains amid streams, creeks, rivers, lakes and forests, where the average annual rainfall is 38.75 inches, more than twice the amount that dry San Berdoo gets.

This is the lake, Oak Lane Reservoir, just a walk down the hill from our house, with our frequent visitor, the lone swan.

The first time I ever saw moss or something green, anyway, growing on a fence or a wall was when I went far away to Dublin, Ireland to study maths (they say "maths" there, rather than "math") for my 3rd year of college at Trinity College. It looked so strange to me, having just come from a desert-like area. The moss-covered concrete steps on the left above were installed on the slope going down the north side of our house by my dear husband way back in 1980 a few months after we'd moved into our house. Thirty years later, they each sport a healthy crop of moss. The steps on the right are newer, only about 2 years old, but I expect they'll be wearing the green within 5 or 10 years.
These concrete steps on the south side of the house are around 20 years old, but they have a long way to go to catch up with the north side steps.
And now, we, too, have moss growing on trees that Jerry planted hundreds of years ago. Here you see it up close and personal on a fruitless mulberry tree...
...and here's the same tree portrait style.
...and here's moss on a willow tree, also planted by Jerry decades ago...
...and here lichen and moss are growing on a large rock...
...and on an oak tree.
...Oh, and I can't overlook that other parasite, mistletoe, which you can see hanging from most oak trees in this area...handy for getting your sweetheart to kiss you.